Fatty acid binding proteins (FABP) are a family of small cytosolic proteins that are abundant in many mammalian tissues and cell-types, including intestine, liver, heart, myelin, and adipocytes. It is generally believed that FABPs play important roles as transporters of free fatty acids (FFA) among intracellular organelles or as intracellular buffers of FFA levels. Their precise role(s) are unknown, however, and the substantial sequence divergence among FABPs from different tissues (as little as 24% identify in some cases) suggests that there may be differential binding and usage of different FFA types among different tissues. The long-term goals of the present studies are (1) to understand the biological function(s) of FABPs, and in particular, the biochemical and biological significance of tissue-specific FABPs; (2) to build at the amino acid level a clear molecular picture describing how binding affinity and specificity are built into FABPs; and (3) to design FABPs with novel binding properties that can be used to construct probes specific for biologically important FFA types. These probes may in the future have important diagnostic applications. Specifically, we will use a fluorescent spectroscopic method to monitor the binding of FFA to FABP. This technology will allow us to measure accurately the thermodynamic and kinetic properties of this binding reaction for a set of distinct FABPs and FFAs. Studies of this kind have not been possible in the past due to the absence of a suitable assay system. We plan to examine the binding of FABPs from the 5 tissues mentioned above (in some cases from both humans and rodents) to FFAs of varying lengths and levels of unsaturation. These studies should provide important clues to the biological role of FABPs. We then plan to dissect further the FABP-FFA interaction by carrying out the same binding studies with specifically designed mutant recombinant FABPs and to use our accumulated experimental results together with computer-aided molecular modeling methods to construct a coherent picture of the FABP-FFA complex. Finally, we plan to use the results of these studies to construct recombinant FABPs with novel FFA binding affinities and specificities.